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Wednesday, 18 January 2012

Cycloid drive


video
Miles Kingsbury reports a 90% efficiency on his cycloid drive:

"We have also found that although the drive is mechanically very efficient, physiologically it was not so good. We did a number of tests and found it was only about 90% as efficient as a circular drive. In the end we decided this inefficiency was caused because the main leg muscles were performing a 50% duty cycle compared with only about half that on a circular drive. Although it seems that this higher duty cycle should help efficiency, it doesn’t allow the muscles to recover and get rid of lactic acid build up, causing a severe burning sensation! ".

I will try to make a multi body analysis of this drive. It may be the problem is the kinetic energy of the thigh, calf and foot at the extreme positions. The cyclist has to do work for decelerating and accelerating his legs at the returns.

A page of Human Power, the technical journal of the IHPVA issue Volume 8 No2, spring 1990

2 comments:

  1. I ride a Thys rowingbike on a regular basis. I use it as my daily commute cycle. Before the rowingbike I rode a lowracer. On the rowingbike I'm as fast as on the lowracer. So I don't have the feeling that I lost a significant amount of efficiency.

    Could this be because on the rowingbike you use a much lower stroke rate than on a bicycle? It is around 45 strokes per minute. Hmm, probably not as the accelerated mass per stroke is also twice as high.

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  2. You can make a rough estimate by assuming all kinetic energy at the start and end of the stroke gets lost. E=1/2.m.v^2

    But the human body is able to adapt and probably this is a too pessimistic approach.

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